1. Wertheim, Journ. f. prakt. Chem. 29, 209 (1843).
2. Winchler, Zeitschr. anal. Chem. 8, 387 (1869).
3. Streng, Oberhess. Gesellsch. f. Natur- u. Heilkunde 22, 258 (1883).
4. Streng, ibid 24, 56 (1886).
5. Behrens, Anleit. z. mikrochem. Analyse, Voss., Leipzig 1895.